Association between serum TSH, free T4 and serum liver enzyme activities in a large cohort of unselected outpatients.

Objective: Although overt thyroid dysfunction is associated with some liver abnormalities, there is a dearth of information on liver function tests across thyroid function tests. We assessed the relationship between serum liver enzyme activity and thyroid function tests in a cohort of adult individuals. Design, patients and measurements: We performed a retrospective analysis on the database of the Clinical Chemistry Laboratory at the Verona University Hospital to retrieve results of serum liver enzyme activities [alanine aminotransferase (ALT), γ-glutamyltransferase (GGT)] and thyroid function tests (TSH and free T4), which have been performed on the whole cohort of outpatient adults consecutively referred by general practitioners for routine blood testing during the last 3 years. Results: Cumulative results for serum GGT, ALT and TSH concentrations were retrieved for 10 292 (68.3% females) outpatient adults with a wide range of age and thyroid function tests. Subjects were categorized according to serum TSH concentrations as follows: < 0.1, 0.1-0.35, 0.36-4.5, 4.6-10 and >10 mU/l. Serum GGT and ALT concentrations increased steadily across the increasing TSH categories (P < 0.0001 for trends), ranging from mean values of 36 to 62 U/l for GGT and from 29 to 41 U/l for ALT, respectively. Similarly, there was a negative, graded, relationship between serum GGT and ALT concentrations and free T4 categories. The results did not change after adjusting for gender, age, lipids and fasting glucose concentrations. Conclusions: Our findings suggest that hypothyroidism and thyroid function tests, even within the reference range, are associated with slightly increased serum GGT and ALT activity concentrations.